In a color facsimile machine having a function for transaction of color documents, the color space has been standardized with L*a*b*, the compression system with JPEG (Joint Photographic Coding Experts Group) or the like, the communication protocol with, for instance, the Group 4 color extension.
In a monochrome type of facsimile machine which is used in a wide range, a received image is generally outputted at a resolution of 240 dpi or 300 dpi. In an outputted image at this resolution, the image is not degraded even if it is copied by a copying machine because the image is monochrome.
As described above, as for an image outputted by the monochrome facsimile machine, a sufficient grade of reproduction thereof can be obtained even if it is copied by a copying machine, and for this reason, when a plurality of copies of a document are required, the plurality of copies in the required grade thereof can be obtained by copying them with the copying machine, which means that it is not required to make the monochrome facsimile machine output a plurality of copies of a document.
However, in a case where an output image obtained by a color facsimile machine from image data transferred in the L*a*b* color space and an output image obtained by color-printing in three colors of Y (Yellow), M (Magenta), and C (Cyan), or in four colors of Y, M, C, and Bk (Black) which is added thereto with a color printer are copied by a copying machine, the image obtained thereby is largely degraded as compared to the monochrome image described above because there is a big difference in a gray scale expression and in a color reproduction system between the color facsimile machine or color printer and the copying machine, which causes the reproduction of the image to be degraded.
Also, in the monochrome facsimile machine described above, in a case of a machine which processes a binary image in black and white, the image is not degraded, however in a case of a machine which processes a multi-valued image in black and white, the output image is expressed in a multi-level of a gray scale (if a black and white gray scale is 8 bits, the gray scale has 256 levels), so that a degree of degradation in an image is affected according to the expression with the gray scale. For this reason, the more multiple levels the gray scale has, the more the reproducibility is degraded.
Furthermore, a data rate of color data for a color facsimile machine as well as of multi-valued data for a monochrome facsimile machine becomes substantially larger as compared to binary data for the monochrome facsimile machine, and especially, a period of time by units of a couple of minutes is required for outputting a color image per sheet in the process of forming a color image by a copying machine. For this reason, in a case where a plurality copies of a color image are outputted by the copying machine, the copying machine is occupied for a long period of time therefor.